Inter national J our nal of Electrical and Computer Engineering (IJECE) V ol. 6, No. 6, December 2016, pp. 3247 3254 ISSN: 2088-8708 3247 Lo w Common-Mode Gain Instrumentation Amplifier Ar chitectur e Insensiti v e to Resistor Mismatches Zainul Abidin 1 , K oichi T anno 2 , Shota Mago 3 , and Hir oki T amura 4 1 Department of Materials and Informatics, Uni v ersity of Miyazaki 2,3 Department of Electrical and System Engineering, Uni v ersity of Miyazaki 4 Department of En vironmental Robotics, Uni v ersity of Miyazaki Article Inf o Article history: Recei v ed Jun 29, 2016 Re vised Aug 18, 2016 Accepted Sep 5, 2016 K eyw ord: instrumentation amplifier dif ferential dif ference amplifier resistor mismatches common-mode v oltage biological signal ABSTRA CT In this paper , an instrumentation amplifier architecture for biological signal is pro- posed. First stage of con v entional instrumentation amplifier architecture w as modified by using fully balanced dif ferential dif ference amplifier and e v aluated by using 1P 2M 0.6 m CMOS process. From HSP ICE simulation result, lo wer common-mode v oltage can be achie v ed by proposed instrumentation amplifier architecture. Actual f abrication w as done and six chips were e v aluated. From the e v aluation result, a v erage common- mode g ain of proposed instrumentation amplifier architecture is 10 : 84 dB lo wer than that of con v entional one without requiring well-matched resistors. Therefore, the pro- posed instrumentation amplifier architecture is suitable for biologica l signal process- ing. Copyright c 2016 Institute of Advanced Engineering and Science . All rights r eserved. Corresponding A uthor: Zainul Abidin Department of Materials and Informatics, Uni v ersity of Miyazaki 1-1, Gakuen Kibanadai Nishi, Miyazaki, 889-2192, Japan zainulelektro@gmail.com 1. INTR ODUCTION Sensor interf ace has considerable interests in medical monitoring and health care systems. Design of the sensor int erf ace circuit has to meet some stringent requirements of analog and digital blocks. Biological signals, such as Electroencephalogram (EEG), Electrooculogram (EOG), Electrocardiogram (ECG), and Elec- tromyogram (EMG) are widely used for medical and health care applications and v ery weak and lo w frequenc y signals. The signals amplitude and frequenc y spans are in the order of V to mV and from DC to a fe w kHz, respecti v ely [1]-[4]. In order to acquire and process the biological signals, Instrumentation Amplifier (IA) is often used [5]. Con v entional IA architecture sho wn in Fig. 1a is often emplo yed to achie v e high signal-to-noise ratio in first block of sensor interf ace [6], [7]. It consists of three operational amplifiers. In this kind of IA architecture, lo w common-mode g ain ( A c ) is necessary and can be achie v ed by satisfying well-matched condition of resistors netw ork. Ho we v er , in actual f abricated chips, resistor mismatch often happens and deteriorates the A c [7]. In this paper , an IA architecture which its A c is lo w and insensiti v e to resistor mismatches is presented. 2. PR OBLEM OF CONVENTION AL INSTR UMENT A TION AMPLIFIER ARCHITECTURE As mentioned in Chapter 1, the IA architecture sho wn in Fig.1a requires well-matched resistors ( R 2 = R 3 , R 4 = R 5 , and R 6 = R 7 ) and the output v oltage of con v entional IA ( V outc ) can be determined as follo ws V outc = R 7 R 5 2 R 3 R 1 + 1 ( V in 2 V in 1 ) (1) J ournal Homepage: http://iaesjournal.com/online/inde x.php/IJECE DOI:  10.11591/ijece.v6i6.11673 Evaluation Warning : The document was created with Spire.PDF for Python.
3248 ISSN: 2088-8708 Figure 1. IA architectures: (a) Con v entional (b) Proposed The V in 1 and V in 2 are defined as v cm v dm and v cm + v dm , respecti v ely ( v cm and v dm are common-mode v oltage and dif ferential input, respecti v ely). Defining resistor mismatch of R i as R i +1 (1 + i +1 ) j i 2 f 2 ; 4 ; 6 g , where i +1 is mismatch rate of R i +1 , V out 1 c and V out 2 c , which are the output v oltages of the first stage, can be gi v en by V out 1 c = 2 R 3 (1 + 3 ) R 1 + 1 v dm + v cm (2) V out 2 c = 2 R 3 R 1 + 1 v dm + v cm (3) Inputting the V out 1 c and V out 2 c to the second stage, which is the subtractor circuit, V outc becomes V outc = R 7 R 5 2 R 3 R 1 (1 + + 3 ) + 1 + v dm + R 7 R 5 ( 1) v cm (4) where is coef ficient defined as follo ws = R 5 + R 7 R 5 (1+ 5 ) 1+ 7 + R 7 (5) From the abo v e deri v ation, the v cm cannot be rejected by the first stage. From Eq. 4, we can find the v cm is amplified due to resistor mismatches of the second stage. Therefore, the resistor mismatches deteriorate the A c . In this w ay , the A c of the con v entional IA architecture is sensiti v e to the resistor mismatches . 3. PR OPOSED INSTR UMENT A TION AMPLIFIER ARCHITECTURE Fig. 1b sho ws the proposed IA architecture. The proposed IA architecture consists of 2 stages; first stage is Fully Balanced Dif ferential Dif ference Amplifier (FBDD A) with 2 ne g ati v e feedbac k resistors and g ain-setting resistor modified from [8] and second stage is as same as the con v entional one. The FBDD A consists of fully dif ferential g ain stage and Common-Mode Feed Back (CMFB) circuit and the output v oltages of FBDD A ( V out 1 p; 2 p ) can be determined by V out 1 p; 2 p = A f ( V in 2 V in 3 ) ( V in 1 V in 4 ) g (6) where A is the amplification of FBDD A, and should be v ery lar ge v alue. Ne xt, theoretical analysis of the proposed IA architecture is presented using the same manner as Chapter 2. Using (6) and the V in 1 ; 2 defined in Chapter 2, under the condition of well-matched resistors, the output v oltage of proposed IA architecture ( V outp ) can be deri v ed as same as Eq. 1 ( V outc ). Otherwise, when resistor mismatches occur , the output v oltages of the first stage ( V out 1 p and V out 2 p sho wn in Fig. 1b) can be deri v ed as IJECE V ol. 6, No. 6, December 2016: 3247 3254 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 3249 Figure 2. Circuit schematic of FBDD A with CMFB circuit follo w V out 1 p = R 3 R 1 (2 + 3 ) + 1 v dm (7) V out 2 p = R 3 R 1 (2 + 3 ) + 1 v dm (8) Therefore, V outp in consideration of resistor mismatches can be gi v en as follo ws. V outp = R 7 R 5 R 3 R 1 (2 + 3 ) + 1 (1 + ) v dm (9) From the abo v e deri v ation, V out 1 p and V out 2 p k eep the balance as sho wn in (7) and (8). Theoretically , v cm is rejected perfectly by the first stage. It confirms that in the second stage, v cm is also rejected perfectly as sho wn in Eq. 9 e v en the resistor mismatches occur . In this case, lo w A c can be achie v ed by the proposed IA architecture. Fig. 2 sho ws the emplo yed FBDD A, which is modified from the reference [8]. The FBDD A consis ts of fully dif ferential g ain stage and common-mode feedback (CMFB) circuit. T w o stages amplifier is emplo yed for the fully dif ferential g ain stage, therefore, phase compensation circuits ( R c 2 , R c 3 , C c 2 and C c 3 ) are added. Furthermore, CMFB circuit is necessary because the FBDD A has dif ferential output. In this design, V c is set to 0 V . The operational amplifier emplo yed in second stage, which is widely used, is sho wn in Fig. 3 [9], [10]. 4. EV ALU A TION In this chapter , simulation result and e v aluation of actual f abricated chip are presented. The IA ar - chitectures were e v aluated using 1P 2M 0 : 6 - m CMOS process. In order to compare the performance of the IA architectures, Fig. 3 w as also emplo yed for AMP1, AMP2, and AMP3 in the con v entional IA architecture. In order to e v aluate the A c , the V in 1 and V in 2 were supplied by v cm which is represented by sine w a v e signal with amplitude of 50 mV and frequenc y of 60 Hz. The resistors netw ork w as designed by R 1 = 51 k and R 2 = R 3 = R 4 = R 5 = R 6 = R 7 = 250 k . Therefore, the ideal total dif ferential g ain is 20 : 7 dB. 4.1. Simulation r esult The IA architectures were simulated using HSPICE. The detailed simulation condition is sho wn in T able 1. Representing resistor mismatches condition ( 3 %), HSPICE si mulation w as done under the mismatch rates 5 and 7 are estimated to 3% and 3% , respecti v ely . The resistors R 4 and R 6 become 242 : 5 k and 257 : 5 k , respecti v ely . Fig. 4a sho ws the FFT simulation result of V outc and V outp . At frequenc y 60 Hz, the Low Common-Mode Gain Instrumentation Amplifier Ar c hitectur e Insensitive to ... (Zainul Abidin) Evaluation Warning : The document was created with Spire.PDF for Python.
3250 ISSN: 2088-8708 Figure 3. Circuit schematic of an operational amplifier v cm of the con v entional and proposed IA architectures reach 57 : 9 dBV and 103 : 5 dBV , respecti v ely . The proposed IA architecture has 45 : 6 dBV lo wer common-mode v oltage than the con v entional one. Monte Carlo simulation w as done by 500 times to get data of A c with de viation of resistor mismatch 3 % ( R 1 R 7 ). Fig. 4b sho ws histogram of A c . A v erage A c of the proposed and con v entional IA architec- tures are 90 : 6 dB and 44 : 9 dB, respecti v ely . The a v erage A c of the proposed IA archi tecture is lo wer than that of the con v entional one. Lastly , the simulated performance of the IA architectures are listed in T able 2. 4.2. Chip e v aluation In order to confirm the actual performance, six chips of the IA architectures were f abricated. Fig. 5 sho ws the microphotograph of the f abricated chip. Due to the number of transistors used in FBDD A, the chip area of the proposed IA architecture is lar ger than that of the con v entional one. Six chips were e v aluated by gi ving v cm in the form of a sine w a v e with 100 mV p p and 60 Hz. Fig. 6 sho ws FFT measurement result of V outc and V outp of chip no. 3 (see T able 3). At the frequenc y of 60 Hz, the V outp and V outc reach 88 dBV and 74 dBV , respecti v ely . It indicates that the v cm of V outp 14 dBV lo wer than that of V outc . Re g arding the gi v en v cm v alue, the A c of the six chips are calculated and summarized in T able 3. A v erage A c of the con v entional and proposed IA architectures ar e 42 : 8 dB and 53 : 64 dB, respecti v ely . From these results, under the condition of actual f abrication result (random resistor mismatches), the A c of the proposed IA architecture is lo wer than that of the con v entional one. The v cm of proposed IA architecture is not perfectl y rejected as mentioned in the theoretical analysis because transistor mism atch w as Figure 4. (a) FFT results of V outc and V outp (b) Histogram of A c (dBV) based on Monte Carlo analysis IJECE V ol. 6, No. 6, December 2016: 3247 3254 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 3251 T able 1. Simulation Condition Items V alue CMOS process 1P 2M 0 : 6 - m CMOS V dd [V] 2 : 5 V ss [V] 2 : 5 V c [V] 0 R bias [k ] 295 M 1 ; 2 [ m/ m] 1 : 3 / 2 , M = 2 M 3 10 [ m/ m] 1 : 3 / 2 , M = 4 M 11 20 [ m/ m] 16 : 1 / 3 , M = 2 M 21 29 [ m/ m] 3 : 3 / 2 , M = 2 R c 1 3 [k ] 9 C c 1 4 [pF] 0 : 5 Note: M means the number of parallel connection T able 2. Summary of the Simulation Results P arameters Con v entional IA Proposed IA A C analysis Dif ferential g ain [dB] 20 : 7 20 : 7 3 dB g ain bandwidth [KHz] 254 : 2 301 : 6 Po wer cons. [W] 596 : 3 843 : 8 Monte Carlo analysis A v e. Ac [dB] 44 : 9 90 : 6 Noise perf ormance (PV) Input ref. noise [ V/ p H z ] 90 : 4 93 : 5 Output ref. noise [ V/ p H z ] 972 : 4 1000 Note: PV = Peak V alue not considered in this paper . Radiated po wer supply noise with frequenc y of 60 Hz is also actual problem. 5. CONCLUSION In this paper , an IA architecture based on FBDD A has been presented. Resistor mismatch which de grades the performance of con v entional IA architecture ha v e been identified and compared in theoretical analysis, simulation and actual chip f abrication. Its ability to achie v e lo w common-mode g ain e v en the resistors are not well-matched mak es it suitable as a part of inte grated circuit for biological signal processing. As other performance parameters, transistor mismatch ef fect and of fs et v oltage cancellation are considered as future w ork. A CKNO WLEDGEMENT This w ork is supported by VLSI Design and Education Center (VDEC), the Uni v ersity of T ok yo in collaboration with Synopsys, Inc. and Cadence Design Systems, Inc. REFERENCES [1] Xiaodan Zou, Xiao yuan Xu, Libin Y ao, and Y ong Lian, ”A 1-V 450-nW fully inte grated programmable biomedical sensor interf ace chip, IEEE J. Solid-State Circuits , v ol. 44, no. 4, pp. 1067-1077, Apr . 2009. [2] Jos Hulzink, et al., ”An Ultra Lo w Ener gy Biomedical Signal Processing System Operating at Near - Threshold”. IEEE T ransactions On Biomedical Circuits And Systems , v ol. 5, no. 6, pp. 546-554, Dec. 2011. [3] Chih-Jen Y en, W en-Y a w Chung and Mely Chen Chi. ”Micro-Po wer Lo w Of fset Instrumentation Amplifier IC Design F or Bio-Medical System Applications”. IEEE T ransactions On Circuits And Systems-I: Re gular Low Common-Mode Gain Instrumentation Amplifier Ar c hitectur e Insensitive to ... (Zainul Abidin) Evaluation Warning : The document was created with Spire.PDF for Python.
3252 ISSN: 2088-8708 Figure 5. Microphotograph of the IA architectures T able 3. A c of the IA Architectures Chip no. Con v entional (dB) Proposed (dB) 1 44 : 97 50 : 97 2 42 : 97 56 : 97 3 44 : 97 58 : 97 4 41 : 97 54 : 97 5 40 : 97 50 : 97 6 40 : 97 48 : 97 P apers , v ol. 51, no. 4, pp. 691-699, Apr . 2004. [4] Akshay Goel and Gurmohan Singh, ”A No v el Lo w Noise High Gain CMOS Instrumentation Amplifier for Biomedical Applications, IAES International Journal of Electri cal and Computer Engineering , v ol. 3, no. 4, pp. 516-523, Aug. 2013. [5] N. V . Helleputte, et al., ”A Multi-P arameter Signal-Acquisition SoC for Connected Personal Health Appli- cations”, IEEE International Solid-State Circuits Conference , pp. 314-315, Febr . 2014. [6] J. Szyno wski, ”CMRR analysis of instrumentation amplifiers, Electronics Letters , v ol. 19, no. 14, pp. 547-549, 1983. [7] Hw ang- Cherng Cho w and Jia -Y u W ang, ”High CMRR instrumentation amplifier for biomedical appli- cation, Proc. IEEE International Symposium on Signal Processing and Its Applications , pp. 1-4, Febr . 2007. [8] A. Hussain and I. Mohammed, A CMOS fully balanced dif ferential dif ference amplifier and its applica- tions, IEEE T rans. on Circuits and Systems-II: Analog and Digital Signal Processing , V ol. 48, No. 6, pp. 614-620, June 2001. [9] P . E. Allen and D. R . Holber g, CMOS Analog Circuit Design , Second Edition. Oxford Uni v ersity Press, Ne w Y ork, 2002. [10] N. Mukahar and S. H. Ruslan, ”A 93.36 dB, 161 MHz CMOS Operational T ransconductance Amplifier (O T A) for a 16 Bit Pipeline Analog-to-Digital Con v ert er (ADC) , IAES International Journal of Electrical and Computer Engineering , v ol. 2, no. 1, pp. 106-111, Feb . 2012. IJECE V ol. 6, No. 6, December 2016: 3247 3254 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 3253 Figure 6. FFT measurement result of chip no. 3 ( V outc and V outp ) BIOGRAPHIES OF A UTHORS Zainul Abidin w as born in 1986. He recei v ed the B. Eng. from Uni v ersity of Bra wijaya and M. Eng. from Uni v ersity of Miyazaki in 2008 and 2011, respecti v ely , and is currently w orking for Uni v ersity of Bra wijaya and to w ard the PhD de gree in Department of Materials and Informatics at Uni v ersity of Miyazaki. He has been in v olv ed with design of analog inte grated circuit since Master De gree. His current research interest includes analog circuit for biological signal processing. He is af filiated with IEEE as student member . K oichi T anno w as born in Miyazaki, Japan, on A pril 22, 1967. He rece i v ed B. E. and M. E . de- grees from the F aculty of Engineering, Uni v ersity of Miyazaki, Miyazaki, Japan, in 1990 and 1992, respecti v ely , and Dr . Eng. de gree from Graduate School of Science and T echnology , K umamoto Uni v ersity , K umamoto, Japan, in 1999. From 1992 to 1993, he joined the Microelectroni cs Prod- ucts De v elopment Laboratory , Hitachi, Ltd., Y ok ohama, Japan. He w as eng aged in research on lo w-v oltage and lo w-po wer equalizer for read channel LSI of hard disk dri v e s. In 1994, he joined Uni v ersity of Miya zaki, where he is currently a Professor in the Department of Electrical and Sys- tems Engineering. His main research interests are in analog inte grated circuit design and multiple- v alued logic circuit design. Dr . T anno is a member of IEEE and the Ex ecuti v e Subcommittee of the IEEE Computer Society T echnical Committee on Multiple-V alued Logic. Shota Mago w as born in 1992. He recei v ed the B.Eng from Uni v ersity of Miyazaki in 2015, and is currently studying to get m aster de gree of Electrical and Electronic Engineering at Uni v ersity of Miyazaki. His current research is Analog CMOS Inte grated Circuits. Low Common-Mode Gain Instrumentation Amplifier Ar c hitectur e Insensitive to ... (Zainul Abidin) Evaluation Warning : The document was created with Spire.PDF for Python.
3254 ISSN: 2088-8708 Hir oki T amura recei v ed the B.E and M.E de gree from Miyazaki Uni v ersity in 1998 and 2000, respecti v ely . From 2000 to 2001, He w as an Engineer in Asahi Kasei Corporation, Japan. In 2001, He joined T o yama Uni v ersity , T o yama, Japan, where He w as a T echnical Of ficial in Department of Intellectual Inf ormation Systems. In 2006, He joined Miyazaki Uni v ersity , Miyazaki, Japan, where He w as an Assistant Professor in Department of Electrical and Electronic Engineering. In 2012, He is currently an Associate Professor in the Department of En vironmental Robotics. His main research interests are Neural Netw orks and Optimization Problems. In recent years, He has the interest in Biomedical Signal Processing using Soft Computing. IJECE V ol. 6, No. 6, December 2016: 3247 3254 Evaluation Warning : The document was created with Spire.PDF for Python.